The present invention relates to pneumatic, radial ply runflat tires and, more specifically, to the wedge-insert reinforced sidewalls of radial ply runflat tires having a metal-reinforced inner ply.
Various methods have been devised for enabling the safe continued operation of unpressurized or underpressurized passenger-car tires without damaging the tire further and without causing poor steering and vehicle handling, over a distance from the place where the tire lost its pressure to a place desired by the driver, such as a service station where the tire can be changed. Loss of tire pressure can result from a variety of causes, including puncture by a foreign object such as a nail or other sharp object piercing the pneumatic tire installed on a vehicle.
Pneumatic tires designed for continued operation under conditions of unpressurization or underpressuration are referred to as extended mobility technology (EMT) tires or simply runflat tires. Runflat tires are capable of being driven in the uninflated condition, whereas the conventional pneumatic tire collapses upon itself when uninflated and supporting a vehicle load. The sidewalls and internal surfaces of EMT tires do not collapse or buckle onto themselves. In general, the terms xe2x80x9cEMTxe2x80x9d and xe2x80x9crunflatxe2x80x9d mean that the tire structure alone has sufficient strength to support the vehicle load when the tire is operated in the uninflated state. In particular, the sidewalls are reinforced to carry the tire""s load without recourse to the use of other supporting structures or devices that are disposed internal to but separate from the tire.
One approach to runflat tire structural design is described in U.S. Pat. No. 4,111,249, entitled the xe2x80x9cBanded Tire,xe2x80x9d in which a wide hoop or annular band approximately as wide as the tread was placed under the tread. The wide hoop in combination with the rest of the tire structure could support the vehicle weight in the uninflated condition.
Numerous other constructions and methods have been used to achieve workable runflat tire designs. Generally, such tires incorporate the reinforced sidewall designs mentioned above. Such sidewalls are thicker and stiffer, so that the tire""s load can be carried by the uninflated tire without otherwise compromising vehicle handling until such reasonable time as the tire can be repaired or replaced. The specific methods used in sidewall stiffening include the incorporation of inserts or fillers generally having, in cross-sectional view, a crescent shape. Such inserts, or wedge inserts as they are often called, are located within the sidewall portion of the tire carcass, which is the region in the tire usually having the lowest rigidity. In such runflat designs, the entire sidewall has an approximately uniform thickness in the region extending radially outward from the bead region to the tire shoulder.
The thick sidewalls of such tires, when operated in the uninflated condition, experience a net compressive load, though the outer portions of the sidewalls are necessarily in tension due to the bending stresses while the inside portions are correspondingly in compression. This is especially the case in the regions of the sidewall that are near the midway point between the tire""s bead region and that portion of the tread most immediately adjacent to the ground-contacting portion of the tread. Due to the large amounts of rubber required to stiffen the sidewall members, heat buildup (deriving from cyclical flexure of the sidewalls) is a major factor in tire failure especially when the tire is operated in the uninflated condition for prolonged periods and at high speeds.
U.S. Pat. No. 5,368,082 (""082), having a common assignee with the present application, disclosed the first commercially accepted runflat pneumatic radial ply tire. The ""082 patent describes the employment of special sidewall inserts to improve stiffness. Approximately six additional pounds of weight per tire was required to support an 800 lb load in this uninflated tire. This earlier invention, although superior to prior attempts at runflat tire design, still imposed a weight penalty that could be offset by the elimination of a spare tire and the tire jack. However, this weight penalty was even more problematic for high-aspect-ratio tires such as those used with large touring sedans. The required supported weight for an uninflated luxury car tire approximates 1400 lbs. These taller sidewalled tires, having-aspect ratios in the 55% to 65% range or greater, means that the sidewall bending stresses are several times those of the earlier low-aspect-ratio runflat tires. Such loads meant that the sidewalls and overall tire had to be stiffened to the point of adversely influencing riding comfort, of luxury vehicles.
Accordingly, the engineering requirements for runflat tire design require that there be none or minimal loss in riding comfort or vehicle handling.
In very stiff suspension performance type vehicles such as sport cars and various sport/utility vehicles, the ability to provide reinforced-sidewall runflat tires was relatively straightforward compared to providing similar runflat tires for luxury sedans requiring a softer ride. Light truck and sport utility vehicles, although not as sensitive to ride performance, provide a runflat tire market that ranges from accepting a stiffer ride to demanding the softer luxury type ride.
Runflat tire design, as disclosed, for example, in U.S. patent application Ser. No. 08/865,489, entitled xe2x80x9cRunflat Tire with Improved Carcass,xe2x80x9d is based on the installation of one or more wedge inserts within each sidewall flex area. The inserts supply the necessary sidewall rigidity in the absence of air pressure during runflat operation. While the high resistance to compression of the compound of the wedge inserts provides the necessary resistance to the collapse of the loaded tire without air pressure, this design has several drawbacks. The two most important ones are increased tire weight and heat buildup in the wedge inserts, especially at high speed and during runflat operation.
During runflat operation, especially at high speed, the heat buildup in the wedge inserts leads to deterioration and disintegrative failure of the tire. Among the methods used to manage heat buildup due to cyclical flexure of the wedge inserts are the use of low-hysteresis rubber compounds in the fabrication of the wedge inserts as well as ways to conduct the heat away from the wedge inserts, as described in EP-A-729,853 incorporated in its entirety by reference herein. Another method by which to minimize heat buildup is to decrease the magnitude of the flexural strain by adding additional rubber to the sidewall-reinforcing wedge inserts or by incorporating additional strengthening structures such as the a metal reinforced first ply, which is able to carry, with minimal deformation, a large portion of the compressive part of each sidewall""s deflected load. An example of a metal-reinforced first ply is disclosed in Patent Application Serial No. PCT/US98/13929, having a common assignee with the present invention. The metal-reinforced first ply carries a large portion of the compressive load on the axially inwardmost side of each wedge insert while also serving to redistribute heat and conduct it away from the insert. Accordingly, a runflat tire incorporating such a metal-reinforced first ply contributes to a longer runflat service life and to improved runflat handling, especially at high speeds.
It is an object of the present invention to provide a light-weight, two-ply runflat radial passenger tire, being as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary objects.
An object of the present invention is to provide a two-ply runflat radial passenger tire, having good tire life and vehicle handling characteristics and a satisfactory ride under normal inflation conditions, by incorporating a compression-load-bearing metallic reinforced inner radial ply that is itself reinforced against compressive buckling by the use of at least one layer of fabric adjacent to the inner ply in the tire""s sidewall regions.
The present invention relates to a pneumatic radial ply runflat tire having a tread, a casing with two sidewalls, two radial carcass plies extending from and wrapped about two annular beads, an inner liner, a wedge insert in each sidewall and a belt reinforcement structure located radially between the tread and the plies. The first or inner carcass ply is reinforced with metal which, in the sidewall regions is sandwiched between two circumferentially disposed fabric treatments each comprising parallel-aligned cords oriented at opposite or crossed angles of between 20 degrees and 50 degrees with respect to each other. The two circumferentially disposed fabric treatments have radial width of between 20 percent and 80 percent of the maximum radial reach of the respective wedge inserts, preferably between 40 percent and 60 percent of the radial reach of the respective wedge inserts.
In a second embodiment, a single woven fabric treatment is circumferentially disposed axially inward of the metal reinforced first or inner carcass ply within each respective sidewall region of the runflat tire. The single woven fabric treatment in each sidewall region has a radial width of between 20 percent and 80 percent of the maximum radial reach of the wedge inserts in the respective sidewall, preferably between 40 percent and 60 percent of the radial reach of the respective wedge inserts.